The present invention relates to a digital frequency synthesizer for generating a frequency-modulated signal and to a radio frequency apparatus including such a device.
It is sometimes necessary to generate a signal having a very accurate phase or frequency modulation. This is, for example, the case with altimeters or telemeters, which use a signal having linear frequency modulation.
The circuits generating such a signal can be produced by purely analog technology, which requires very high quality components, or by digital technology using programmable phase shifters, as in U.S. Pat. No. 4,160,958. Apart from its complexity of construction, the latter method suffers from the main disadvantage of using a programmable phase shifter, which is an analog precision element and whose construction is particularly difficult when requiring a high stability in both temperature and time.